The HD 5770 graphics card is possibly the culprit for you performance loss, since it only have 1GB of VRAM and, well, it's quite old (2009/2010 architecture). All the rest of your machine specs are top tier and should deliver blazing fast speeds regardless of file sizes. That card is definitely your bottleneck. If you can, switch to any recent nVidia board with at least 4GB of VRAM (a GTX 1050 or 1060 should do it) and you will experience a great jump in productivity. The CUDA cores themselves are reason enough to switch to nVidia, since most of the operations are done much faster in those than on you processor cores.

OK, sounds like problem-solution>>>buy a new graphic card. Of course I'm considering this upgrade, but... I foud some dilemma before I buy a new GP. Did You make this kind of upgrade by Yourself or someone You know personally did? And after that said that everything is fine now? Never found this kind of data.

Why I'm so sceptical? Same issues i'm having on my MBP with 2GB VRAM 16 GB RAM and 2,4 GHz i7. Same issues are present in my company partner Windows Dell 4,2 GHz with nVidia Quadro 16 GB VRAM 64 GB RAM? Why same issues I'm reading about on Adobe Community forum for newest serious computers? Having an idea? Anyway thank You very, very much for answering and for sure good intensions. Cheers Eduardo!